Polyhydroxy curable fluoroelastomer compositions

ABSTRACT

Disclosed herein is a curable composition comprising a polyhydroxy curable fluoroelastomer, a polyhydroxy curative, a cure accelerator and an unsaturated metal compound process aid. Such curable compositions have a lower Mooney viscosity than do similar compositions absent the process aid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/570,873 filed Dec. 15, 2011.

FIELD OF THE INVENTION

This invention relates to polyhydroxy curable fluoroelastomercompositions comprising i) a fluoroelastomer, ii) a polyhydroxycurative, iii) a cure accelerator and iv) an unsaturated metal compoundprocess aid.

BACKGROUND OF THE INVENTION

Fluoroelastomers having excellent heat resistance, oil resistance, andchemical resistance have been used widely for sealing materials,containers and hoses. Examples of fluoroelastomers include copolymerscomprising units of vinylidene fluoride (VF₂) and units of at least oneother copolymerizable fluorine-containing monomer such ashexafluoropropylene (HFP), tetrafluoroethylene (TFE),chlorotrifluoroethylene (CTFE), vinyl fluoride (VF), and a fluorovinylether such as a perfluoro(alkyl vinyl ether) (PAVE). Specific examplesof PAVE include perfluoro(methyl vinyl ether), perfluoro(ethyl vinylether) and perfluoro(propyl vinyl ether).

In order to fully develop physical properties such as tensile strength,elongation, and compression set, elastomers must be cured, i.e.vulcanized or crosslinked. In the case of fluoroelastomers, this isgenerally accomplished by mixing uncured polymer (i.e. fluoroelastomergum) with a polyfunctional curing agent and heating the resultantmixture, thereby promoting chemical reaction of the curing agent withactive sites along the polymer backbone or side chains. Interchainlinkages produced as a result of these chemical reactions causeformation of a crosslinked polymer composition having athree-dimensional network structure. Commonly employed curing agents forfluoroelastomers include difunctional nucleophilic reactants, such aspolyhydroxy compounds.

Prior to curing, fluoroelastomers are typically compounded with otheringredients (e.g. fillers, colorants, etc.) and shaped (e.g. molded orextruded) into various articles such as seals, o-rings, gaskets andhose. Fluoroelastomer compositions may have a Mooney viscosity that istoo high to mix or shape easily. Thus, it would be desirable to havemeans to lower the Mooney viscosity of fluoroelastomer compositions.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a curable fluoroelastomercomposition comprising:

A) a polyhydroxy curable fluoroelastomer;

B) a polyhydroxy curative;

C) a cure accelerator; and

D) an unsaturated metal compound process aid having the formulaY_((4-n))MX_(n) wherein Y is selected from alkyl, aryl, carboxylic acid,or alkyl ester groups; M is selected from Si, Ge, or Sn; X is an allylgroup CR¹R²CR³═CR⁴R⁵, vinyl group CR¹═CR²R³, allenyl group CR¹═C═CR²R³,alkynyl group C≡CR¹, or propargyl group CR¹R²C≡CR³; R¹-R⁵ are selectedindependently from the group consisting of H, F, alkyl, aryl,heterocycle, or perfluoroalkyl groups; and n is 1, 2, or 3.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to polyhydroxy curable fluoroelastomercompositions that contain an unsaturated metal compound process aid.Such fluoroelastomer compositions have a lower Mooney viscosity than dosimilar compositions absent the process aid.

Fluoroelastomers that are suitable for use in this invention are thosethat are polyhydroxy curable. By “polyhydroxy curable” is meantfluoroelastomers which are known to crosslink with polyhydroxy curativessuch as bisphenol AF. Such fluoroelastomers include those having aplurality of carbon-carbon double bonds along the main elastomer polymerchain and also fluoroelastomers which contain sites that may be readilydehydrofluorinated. The latter fluoroelastomers include, but are notlimited to those which contain adjacent copolymerized units ofvinylidene fluoride (VF₂) and hexafluoropropylene (HFP) as well asfluoroelastomers which contain adjacent copolymerized units of VF₂ (ortetrafluoroethylene) and a fluorinated comonomer having an acidichydrogen atom such as 2-hydropentafluoropropylene;1-hydropentafluoropropylene; trifluoroethylene;2,3,3,3-tetrafluoropropene; or 3,3,3-trifluoropropene. Preferredfluoroelastomers include the copolymers of i) vinylidene fluoride withhexafluoropropylene and, optionally, tetrafluoroethylene (TFE); ii)vinylidene fluoride with a perfluoro(alkyl vinyl ether) such asperfluoro(methyl vinyl ether), 2-hydropentafluoropropylene andoptionally, tetrafluoroethylene; iii) tetrafluoroethylene with propyleneand 3,3,3-trifluoropropene; iv) tetrafluoroethylene, perfluoro(methylvinyl ether) andhexafluoro-2-(pentafluorophenoxy)-1-(trifluorovinyloxy)propane, and v)ethylene with tetrafluoroethylene, perfluoro(methyl vinyl ether) and3,3,3-trifluoropropylene.

In addition to the fluoroelastomer, curable compositions of thisinvention contain a polyhydroxy cure system, meaning a polyhydroxycurative and a vulcanization (or curing) accelerator.

The curable compositions contain 0.4 to 4 parts by weight (preferably 1to 2.5 parts) of polyhydroxy curing agent (or a derivative thereof) per100 parts by weight fluoroelastomer, i.e. 0.4-4 phr (preferably 1-2.5phr). Typical polyhydroxy cross-linking agents include di-, tri-, andtetrahydroxybenzenes, naphthalenes, and anthracenes, and bisphenols ofthe formula

where A is a difunctional aliphatic, cycloaliphatic, or aromatic radicalof 1-13 carbon atoms, or a thio, oxy, carbonyl, sulfinyl, or sulfonylradical; A may optionally be substituted with at least one chlorine orfluorine atom; x is 0 or 1; n is 1 or 2; and any aromatic ring of thepolyhydroxylic compound may optionally be substituted with at least onechlorine or fluorine atom, an amino group, a —CHO group, or a carboxylor acyl radical. Preferred polyhydroxy compounds includehexafluoroisopropylidene-bis(4-hydroxy-benzene) (i.e. bisphenol AF orBPAF); 4,4″-isopropylidene diphenol (i.e. bisphenol A);4,4″-dihydroxydiphenyl sulfone; and diaminobisphenol AF. Referring tothe bisphenol formula shown above, when A is alkylene, it can be forexample methylene, ethylene, chloroethylene, fluoroethylene,difluoroethylene, propylidene, isopropylidene, tributylidene,heptachlorobutylidene, hepta-fluorobutylidene, pentylidene, hexylidene,and 1,1-cyclohexylidene. When A is a cycloalkylene radical, it can befor example 1,4-cyclohexylene, 2-chloro-1,4-cyclohexylene,cyclopentylene, or 2-fluoro-1,4-cyclohexylene. Further, A can be anarylene radical such as m-phenylene, p-phenylene, o-phenylene,methylphenylene, dimethylphenylene, 1,4-naphthylene,3-fluoro-1,4-naphthylene, and 2,6-naphthylene. Polyhydroxyphenols of theformula

where R is H or an alkyl group having 1-4 carbon atoms or an aryl groupcontaining 6-10 carbon atoms and R′ is an alkyl group containing 1-4carbon atoms also act as effective crosslinking agents. Examples of suchcompounds include hydroquinone, catechol, resorcinol,2-methylresorcinol, 5-methyl-resorcinol, 2-methylhydroquinone,2,5-dimethylhydroquinone, 2-t-butyl-hydroquinone; and such compounds as1,5-dihydroxynaphthalene and 2,6-dihydroxynaphthalene.

Additional polyhydroxy curing agents include alkali metal salts ofbisphenol anions, quaternary ammonium salts of bisphenol anions,tertiary sulfonium salts of bisphenol anions and quaternary phosphoniumsalts of bisphenol anions. For example, the salts of bisphenol A andbisphenol AF. Specific examples include the disodium salt of bisphenolAF, the dipotassium salt of bisphenol AF, the monosodium monopotassiumsalt of bisphenol AF and the benzyltriphenylphosphonium salt ofbisphenol AF.

Quaternary ammonium and phosphonium salts of bisphenol anions arediscussed in U.S. Pat. Nos. 4,957,975 and 5,648,429. Bisphenol AF salts(1:1 molar ratio) with quaternary ammonium ions of the formulaR₁R₂R₃R₄N⁺, wherein R₁-R₄ are C₁-C₈ alkyl groups and at least three ofR₁-R₄ are C₃ or C₄ alkyl groups are preferred. Specific examples ofthese preferred compositions include the 1:1 molar ratio salts oftetrapropyl ammonium-, methyltributylammonium- and tetrabutylammoniumbisphenol AF. Such salts may be made by a variety of methods. Forinstance a methanolic solution of bisphenol AF may be mixed with amethanolic solution of a quaternary ammonium salt, the pH is then raisedwith sodium methoxide, causing an inorganic sodium salt to precipitate.After filtration, the tetraalkylammonium/BPAF salt may be isolated fromsolution by evaporation of the methanol. Alternatively, a methanolicsolution of tetraalkylammonium hydroxide may be employed in place of thesolution of quaternary ammonium salt, thus eliminating the precipitationof an inorganic salt and the need for its removal prior to evaporationof the solution.

In addition, derivatized polyhydroxy compounds such as mono- ordiesters, and trimethylsilyl ethers are useful crosslinking agents.Examples of such compositions include, but are not limited to resorcinolmonobenzoate, the diacetate of bisphenol AF, the diacetate of sulfonyldiphenol, and the diacetate of hydroquinone.

Vulcanization accelerators (also referred to as cure accelerators) whichmay be used in the curable fluoroelastomer compositions include tertiarysulfonium salts such as [(C₆H₅)₂S⁺(C₆H₁₃)][Cl]⁻, and[(C₆H₁₃)₂S(C₆H₅)]⁺[CH₃CO₂]⁻ and quaternary ammonium, phosphonium,arsonium, and stibonium salts of the formula R₅R₆R₇R₈Y⁺X⁻, where Y isphosphorous, nitrogen, arsenic, or antimony; R₅, R₆, R₇, and R₅ areindividually C₁-C₂₀ alkyl, aryl, aralkyl, alkenyl, and the chlorine,fluorine, bromine, cyano, —OR, and —COOR substituted analogs thereof,with R being C₁-C₂₀ alkyl, aryl, aralkyl, alkenyl, and where X ishalide, hydroxide, sulfate, sulfite, carbonate,pentachlorothiophenolate, tetrafluoroborate, hexafluorosilicate,hexafluorophosphate, dimethyl phosphate, and C₁-C₂₀ alkyl, aryl,aralkyl, and alkenyl carboxylates and dicarboxylates. Particularlypreferred are benzyltriphenylphosphonium chloride,benzyltriphenylphosphonium bromide, tetrabutylammonium hydrogen sulfate,tetrabutylammonium hydroxide, tetrapropylammonium hydroxide,tetrabutylammonium bromide, tributylallylphosphonium chloride,tributyl-2-methoxypropylphosphonium chloride,1,8-diazabicyclo[5.4.0]undec-7-ene, andbenzyldiphenyl(dimethylamino)phosphonium chloride. Other usefulaccelerators include methyltrioctylammonium chloride,methyltributylammonium chloride, tetrapropylammonium chloride,benzyltrioctylphosphonium bromide, benzyltrioctylphosphonium chloride,methyltrioctylphosphonium acetate, tetraoctylphosphonium bromide,methyltriphenylarsonium tetrafluoroborate, tetraphenylstibonium bromide,4-chlorobenzyltriphenyl phosphonium chloride,8-benzyl-1,8-diazabicyclo(5.4.0)-7-undecenonium chloride,diphenylmethyltriphenylphosphonium chloride, allyltriphenyl-phosphoniumchloride, tetrabutylphosphonium bromide,m-trifluoromethyl-benzyltrioctylphosphonium chloride, and otherquaternary compounds disclosed in U.S. Pat. Nos. 5,591,804; 4,912,171;4,882,390; 4,259,463; 4,250,278 and 3,876,654. The amount of acceleratorused is between 0.05 and 2 parts by weight per hundred parts by weightfluoroelastomer (0.05-2 phr). Preferably, 0.1 to 1.0 parts acceleratorper hundred parts fluoroelastomer is used.

The curable compositions of the invention also contain between 0.1 and 4(preferably 0.3 to 2) parts by weight of at least one unsaturated metalcompound process aid per 100 parts fluoroelastomer.

The process aid has the formula Y_((4-n))MX_(n) wherein Y is selectedfrom alkyl, aryl, carboxylic acid, or alkyl ester groups; M is selectedfrom Si, Ge, or Sn; X is an allyl group CR¹R²CR³═CR⁴R⁵, vinyl groupCR¹═CR²R³, allenyl group CR¹═C═CR²R³, alkynyl group C≡CR¹, or propargylgroup CR¹R²C≡CR³; R¹-R⁵ are selected independently from the groupconsisting of H, F, alkyl, aryl, heterocycle, or perfluoroalkyl groups;and n is 1, 2, or 3. The R¹-R⁵ group may be a mixed alkyl andperfluoroalkyl group such as CF₃(CF₂)₅CH₂CH₂—. Preferred for Y groupsare phenyl groups or alkyl groups. Most preferred Y groups are alkylgroups, particularly where each alkyl group has 4, 6 or 8 carbon atoms.Carboxylic acid Y groups can be for example octanoic or stearic acid ora diacid such as maleic acid. Allyl and vinyl groups are preferred for Xand allyl is most preferred. It is preferred that n is 1 or 2 and mostpreferred that n is 1. It is preferred that the R¹-R⁵ groups be H or Fand most preferably H. Introduction of an excess of non-hydrogen Rgroups on the unsaturated X group can be detrimental to performance dueto steric hindrance. However introduction of 1, 2 or 3 non-hydrogengroups can in some instances improve performance. The syntheses ofunsaturated tin compounds is described for example in OrganotinChemistry, 2nd Ed. (Wiley-VCH, 2004, Weinheim, Germany, Alwyn G. Daviesauthor). Specific examples of unsaturated metal compound coagentssuitable for use in this invention include, but are not limited toallyltributyltin, methallyltri-n-butyltin, diallyldibutyltin,allyltriphenyltin, tributyl(vinyl)tin, diallyldioctyltin,allyltriphenylstannane, allyltriphenylgermane, vinyltriphenyltin,allyltriphenylsilane, allyltrioctylstannane, allyltrioctylgermane,vinyltrioctylstannane, divinyldioctylstannane, andtriphenyl(vinyl)silane.

Without being bound by theory, the reduction in viscosity is believed tobe caused by association of polar polymer end groups such as carboxylicor sulfonic acids or their salts with the unsaturated metal compoundprocess aid forming a species that has weaker ionic interchainassociations and thus lower viscosity.

Other ingredients (e.g. fillers, colorants, process aids, acidacceptors, etc.) commonly employed in elastomer compositions may also beincluded in the curable compositions of the invention.

The fluoroelastomer, polyhydroxy curative, cure accelerator, unsaturatedmetal compound process aid and any other ingredients are generallyincorporated into a curable composition by means of an internal mixer orrubber mill. The resulting composition may then be shaped (e.g. moldedor extruded) and cured to form a fluororubber article. Curing typicallytakes place at about 150°-200° C. for 1 to 60 minutes. Conventionalrubber curing presses, molds, extruders, and the like provided withsuitable heating and curing means can be used. Also, for optimumphysical properties and dimensional stability, it is preferred to carryout a post curing operation wherein the molded or extruded fluororubberarticle is heated in an oven or the like for an additional period ofabout 1-48 hours, typically from about 180°-275° C., generally in an airatmosphere.

EXAMPLES Test Methods

Mooney viscosity was determined according to ASTM D-1646, large rotor,condition ML 1+10 minutes, measured at 121° C.

-   -   Cure characteristics were measured using a Monsanto Moving Die        Rheometer (MDR 2000) instrument under the following conditions:

Moving die frequency: 1.66 Hz

Oscillation amplitude: 0.5

Temperature: 177° C. unless otherwise indicated

Duration of test: 24 minutes

-   -   The following cure parameters were recorded:

M_(H): maximum torque level, in units of dN·m

M_(L): minimum torque level, in units of dN·m

t_(s)2: minutes to 2 units rise above M_(L)

t50: minutes to 50% of maximum torque

t90: minutes to 90% of maximum torque

Tensile properties were determined by ASTM D412.

Compression set resistance was measured according to ASTM D395.

The invention is further illustrated by, but is not limited to, thefollowing examples.

Fluoroelastomer (FKM1) employed in the examples was Viton® VTR-7241, acopolymer of vinylidene fluoride, hexafluoropropylene, andtetrafluoroethylene, available from DuPont.

Example 1 and Comparative Examples A-C

Curable compositions for Example 1 and Comparative Examples A-C weremade by compounding the ingredients on a two-roll mill.

Formulations are shown in Table I. Mooney viscosity of the compositionsis also shown in Table I. A substantial (27.4%) reduction in Mooneyviscosity was observed with allyltributyltin process aid of thisInvention (Example 1), while only a minor decrease (1.6-3.9%) in Mooneyviscosity was noted for dioctyltin oxide and dibutyltin dilaurate inComparative Examples B and C.

TABLE I Comp. Comp. Comp. Ingredient, phr¹ Ex. 1 Ex. A Ex. B Ex. C FKM1100 100 100 100 Ca(OH)₂ 6 6 6 6 MgO² 3 3 3 3 Allyltributyltin 1 0 0 0Dioctyltin oxide 0 0 1 0 Dibutyltindilaurate 0 0 0 1 Carbon black 30 3030 30 N990 VC50³ 2.5 2.5 2.5 2.5 Microcel E⁴ 1 0 0 0 Mooney viscosity,91.1 125.4 123.4 120.5 ML(1 + 10) @121° C. Curing Characteristics (177°C./24 min.) ML, dNm 1.41 1.89 1.76 1.93 MH, dNm 20 17.52 16.62 21.33ts2, minutes 1.82 4.54 2.73 3.31 t50, minutes 2.17 5.65 3.45 4.38 t90,minutes 2.84 8.19 4.63 5.61 Compression set, 25% Deflection Compression65 51 66 59 Set 200° C., 70 h, % Physical Properties Hardness, Shore A83 76 80 83 M50, MPa 3.26 2.61 2.95 3.27 M100, MPa 5.19 4.36 4.44 5.14M200, MPa 10.32 8.62 8.7 9.78 Tb, MPa 12.29 12.34 12.16 12.6 Eb (%) 261337 312 294 Tensile (20°) Hot Air Aged 168 h/250° C. Hardness, 99% 101% 98% 99% % retention M50, % retention 82% 89% 76% 84% M100, 59% 79% 63%63% % retention Tb, % retention 45% 66% 42% 47% Eb, % retention 153% 107%  131%  148%  ¹parts by weight per hundred parts rubber (i.e.fluoroelastomer) ²Elastomag 170, (available from Akrochem Corp.) ³amixture of bisphenol AF and a quaternary phosphonium salt (availablefrom DuPont) ⁴Calcium metasilicate (available from Celite Corporation)

Example 2-3 and Comparative Example D

Curable compositions for Examples 2-3 and Comparative Example D weremade by compounding the ingredients on a two-roll mill. Formulations areshown in Table 2. Mooney viscosity of the compositions is also shown inTable 2. Mooney viscosity was reduced 9.7-12.1% by the silanes of thisInvention.

TABLE 2 Comp. Ingredient, phr¹ Ex. D Example 2 Example 3 FKM1 100 100100 Ca(OH)₂ 6 6 6 MgO² 3 3 3 Allyltriphenylsilane 0 1 0Triphenyl(vinyl)silane 0 0 1 Carbon black N990 30 30 30 VC50³ 2.5 2.52.5 Mooney viscosity, 117.1 102.9 105.7 ML(1 + 10) @121° C. CuringCharacteristics (190° C./30 min.) ML, dNm 1.24 1.17 1.26 MH, dNm 17.0216.85 17.53 ts2, minutes 2.71 2.33 2.14 t50, minutes 3.4 2.87 2.63 t90,minutes 4.56 3.73 3.41 Compression set, 25% Deflection Compression Set36 33 37 200° C., 70 h, % Physical Properties Hardness, Shore A 71 72 74M50, MPa 2.12 2.13 2.4 M100, MPa 3.76 3.92 4.26 M200, MPa 9.14 9.45 9.81Tb, MPa 12.96 10.91 13.04 Eb (%) 269 221 260 Tensile (20°) Hot Air Aged70 h/275° C. Hardness, 101%  100%  100%  % retention M50, % retention86% 86% 83% M100, % retention 70% 65% 62% M200, % retention 54% 51% 46%Tb, % retention 71% 80% 59% Eb, % retention 137%  167%  160%  ¹parts byweight per hundred parts rubber (i.e. fluoroelastomer) ²Elastomag 170,(available from Akrochem Corp.) ³a mixture of bisphenol AF and aquaternary phosphonium salt (available from DuPont)

What is claimed is:
 1. A curable fluoroelastomer composition comprising:A) a polyhydroxy curable fluoroelastomer; B) a polyhydroxy curative; C)a cure accelerator; and D) an unsaturated metal compound process aidhaving the formula Y_((4-n))MX_(n) wherein Y is selected from alkyl,aryl, carboxylic acid, or alkyl ester groups; M is selected from Si, Ge,or Sn; X is an allyl group CR¹R²CR³═CR⁴R⁵, vinyl group CR¹═CR²R³,allenyl group CR¹═C═CR²R³, alkynyl group C≡CR¹, or propargyl groupCR¹R²C≡CR³; R¹-R⁵ are selected independently from the group consistingof H, F, alkyl, aryl, heterocycle, or perfluoroalkyl groups; and n is1,2, or
 3. 2. The curable composition of claim 1 wherein saidunsaturated metal compound process aid is of the formula Y_((4-n))MX_(n)wherein M is Sn, X is allyl group CR¹R²CR³═CR⁴R⁵, Y is alkyl or aryl,R¹-R⁵ are H and n is 1 or
 2. 3. The curable composition of claim 2wherein said unsaturated metal compound process aid isallyltrioctylstannane.
 4. The curable composition of claim 2 whereinsaid unsaturated metal compound process aid is allyltriphenylstannane.5. The curable composition of claim 2 wherein said unsaturated metalcompound process aid is diallyldioctylstannane.
 6. The curablecomposition of claim 1 wherein said unsaturated metal compound processaid is of the formula Y_((4-n))MX_(n) wherein M is Sn, X is vinyl groupCR¹═CR²R³, Y is alkyl or aryl, R¹-R³ are H and n is
 1. 7. The curablecomposition of claim 6 wherein said unsaturated metal compound processaid is vinyltrioctylstannane.
 8. The curable composition of claim 6wherein said unsaturated metal compound process aid isvinyltriphenylstannane.
 9. The curable composition of claim 1 whereinsaid unsaturated metal compound process aid is of the formulaY_((4-n))MX_(n) wherein M is Ge, X is allyl group CR¹R²CR³═CR⁴R⁵, Y isalkyl or aryl, R¹-R⁵ are H and n is
 1. 10. The curable composition ofclaim 9 wherein said unsaturated metal compound process aid isallyltrioctylgermane.
 11. The curable composition of claim 9 whereinsaid unsaturated metal compound process aid is allyltriphenylgermane.12. The curable composition of claim 1 wherein said unsaturated metalcompound process aid is of the formula Y_((4-n))MX_(n) wherein M is Si,X is allyl group CR¹R²CR³═CR⁴R⁵, Y is alkyl or aryl, R¹-R⁵ are H and nis
 1. 13. The curable composition of claim 12 wherein said unsaturatedmetal compound process aid is allyltriphenylsilane.
 14. The curablecomposition of claim 1 wherein said unsaturated metal compound processaid is of the formula Y_((4-n))MX_(n) wherein M is Si, X is vinyl groupCR¹═CR²R³, Y is alkyl or aryl, R¹-R³ are H and n is
 1. 15. The curablecomposition of claim 14 wherein said unsaturated metal compound processaid is triphenyl(vinyl)silane.